Large variation in the causes of childhood obesity worldwide

While childhood obesity rates have plateaued in the US, they continue to climb in countries across East Asia, the Middle East, North Africa, and South Asia

The risk for metabolic disease associated with childhood obesity is not a function of body mass index, according to the paper, but of how and where the body stores fat

The factors causing childhood obesity are different for wealthier and poorer countries, and the management of the disease is complex, according to a report by Yale scientists. According to one study cited in the report, BMI data from 200 countries showed paediatric obesity has risen from 4% in 1975 to 18% in 2016 or from 5 million to 50 million girls and 6 million to 74 million boys. While childhood obesity rates have plateaued in the US, they continue to climb in countries across East Asia, the Middle East, North Africa, and South Asia (children who meet the definition of having obesity have BMIs of 85% or 95% above average).

"In poorer countries, we're seeing not only a rise in childhood obesity, but in parallel with malnutrition," said lead author, Dr Sonia Caprio, professor of pediatrics (endocrinology) at Yale School of Medicine, and one of the report's authors. "In the US, the problem is inertness, but there is more awareness about the dangers of consumption of sugar and soda. In China, India, and South America, they are pushing these products and soda consumption is very high. And the water is not drinkable."

The paper, ‘Childhood obesity and the associated rise in cardiometabolic complications’, published in Nature Metabolism, focused on understanding the mechanism that causes Type 2 diabetes. The risk for metabolic disease associated with childhood obesity is not a function of body mass index, according to the paper, but of how and where the body stores fat.

In her clinic, Caprio used MRI scans of patients to discover that children with obesity who are prone to metabolic diseases such as fatty liver disease and cardiovascular disease have a layer of subcutaneous fat that is thinner than average. Unable to store the excess abdominal fat in that layer, the body pushes it into other tissues in the body, including as fat droplets in the liver.

"The liver then becomes inflamed and contributes to the development of insulin resistance," explained Caprio. In one ten-year multinational trial, Caprio found that patients who present with thinner subcutaneous fat "are marching to cardiovascular complications six to seven years down the road, including hypertension and kidney disease," the report stated.

From 2002-2012, type 2 diabetes rose by 4.8% among youth under 20, according to a study by the Centers for Disease Control and the National Institutes of Health, and type 2 diabetes is more aggressive in children than adults, said Caprio.

"With kids, it is very difficult to reach a glucose level that is satisfactory and controlled," she said. "And the drugs that adults use to manage glucose are not yet approved for kids."

Further complicating matters, added Caprio, is that childhood obesity often develops into Type 2 diabetes during the teenage years, when controlling a child's diet can be challenging. And, she noted: "Puberty is a time when insulin resistance is already very high."

The only way to mitigate obesity is better nutrition, Caprio concludes, but dietary options for kids tend toward "carbs and highly enriched processed food."

She added that rates are plateauing in the US, due in large part to broader awareness. That public education effort needs to be expanded to further curb rates in the US and abroad, she said.

"There has been a change in the perception of obesity as being more than just a cosmetic problem," Caprio said. "Compared to 10 or 15 years ago, we're in a much better situation of knowledge of the problem."